Detecting wear of electrical conductors such as insulated wires and conduits such as plastic pipes and hoses is important early detection of wear can lead to prevention of a system failure. For example, a conduit such as a plastic pipe for carrying a liquid such as water includes an outer surface, an inner surface and a wall having a thickness defined by the inner and outer surfaces. The inner surface also defines a fluid flow path. When the conduit is placed within the ground, usually three to four feet below the surface of the earth, the outer surface of the plastic pipe is exposed to the earth and will wear due to natural forces occurring within the earth. Wear also occurs along the inner surface of the pipe due to the flow of water within the pipe. As the outer and inner surfaces of the plastic pipe wear, the wall defined by the outer and inner surfaces decreases in thickness and eventually may wear completely through. If this occurs, the water flowing through the pipe will escape into the earth and a costly repair process must be performed in order to restore operation.
In order to minimize the possibility of complete failure of a system, plastic pipe and the like usually are replaced in accordance with a predetermined time schedule. More specifically, the pipe is replaced, for example, when 60% of its calculated useful life has expired. Therefore, plastic pipe and the like, which may have an actual remaining useful life of many years, generally will be replaced regardless of its condition. Replacement processes thus generally are more qualitative, e.g. the pipe is old, rather than quantitative, e.g. the pipe has worn to a certain point. This replacement process leads to waste, for example, because conduits may be replaced even though only a small percentage of their actual useful life has expired.
The above example with regard to plastic pipe used to carry water is for illustrative purpose only. For example, such wear occurs in steel pipes and other conduits. Electrical conductors such as insulated wire also undergo wear. Specifically, the insulation surrounding the conductive wire eventually may wear through. Wear detection therefore is useful in many fields and is not limited to any particular field.
Further, wear detection is a time-consuming task. For example, the task of inspecting wires for wear in a single airplane is very time-consuming, sometimes requiring miles of wire to be inspected by hand. Also, inspecting plastic pipe for wear is time-consuming. Specifically, one end of the pipe is sealed with a plug and the other end of the pipe has an air pump and air guage sealed thereto. The air pump is then operated so that the pipe is pumped with air to a certain minimum air pressure. Then, the air pressure within the pipe is checked, over a period of time, to determine whether the air pressure has decreased, i.e. whether air is leaking from the pipe. If the air pressure does decrease, the pipe may be worn to a point beyond its useful life. The air pressure decrease also may indicate that the pipe was not properly sealed at its ends or that the air gauge being used to measure the pressure is faulty. Therefore, if air pressure decreases, the air pressure test process generally is repeated at least once. This process is costly both in terms of time and equipment. Decreasing the costs and time required to inspect conduits and wires therefore could lead to substantial savings.
Known systems for detecting wear include systems such as the one described in U.S. Pat. No. 4,735,083. The above-identified patent describes a conduit for carrying liquid, the conduit including inner and outer surfaces and a dye disposed between the surfaces. When liquid flowing through the conduit acquires the color of the dye, the conduit should be replaced. With the system described in U.S. Pat. No. 4,735,083, if the outer surface wears faster than the inner surface, the dye may be discharged into, for example, the earth without providing a system user any indication of wear. Also, if the system described above is utilized in a water supply conduit for drinking water, discoloration of the water may be extremely undesirable.
It is therefore an object of the present invention to provide a system for detecting wear of articles, the system providing a qualitative indication as to wear.
Another object of the present invention is to provide a system for detecting wear of articles which provides an indication as to wear of an outer and/or an inner surface of the article.
Still another object of the present invention is to provide a system for detecting wear of articles which allows relatively fast inspection and detection.